A fundamental biological process in animal cells is the establishment of cell polarity. Cell polarization results in an asymmetric segregation of cell determinants and this, in turn, allows daughter cells to proceed toward different cell fates. The C. elegans embryo is an ideal system for understanding cell polarity due to the easily observed asymmetric divisions that occur during early development, when cells are quite large. Cell biology, genetic, and experimental approaches will be used to characterize the role of non-muscle myosin II (NMY-2) during cytokinesis and the establishment of cell polarity. To analyze the role of NMY-2 in polarity, Green Fluorescent Proteins and RNA interference will be used to localize NMY-2 and determine its phenotype, respectively. To understand NMY-2 function, it is necessary to identify proteins which interact with NMY-2 and MLC-4 using the yeast two-hybrid system. This will identify proteins that determine the proper localization and function of NMY-2 through direct interactions with NMY-2 or via MLC-4. Chromosome 1 RNAi feeding vectors will be used to screen for cytokinesis mutants in a double mutant background for proteins that regulate the contractile activities of NMY-2. The studies proposed here will contribute to understanding the function and regulation of NMY-2 in polarity and its contractile activity in cytokinesis.